Which explanation is mostly likely the reason for the evolution of a larger brain in humans

Two different answers:

Answer A

"A large brain allows humans to solve complex problems. This, in turn, has allowed humans with bigger brains to survive better than humans with smaller brains." By austinmcdowell

Answer B

"Across nearly seven million years, the human brain has tripled in size. The most likely the reason for the evolution of a larger brain in humans is that a larger brain allows humans to solve complex problems. Large, complex brains enable humans to process and store a lot of information and to interact with each other and with their surroundings better. The brain we now humans have is the largest and most complex of any living primate." By LearnGrow